JPH0522572B2 - - Google Patents

Description

[Detailed description of the invention]

FIELD OF THE INVENTION This invention relates to filler-containing biaxially oriented polyester films with improved surface properties, and in particular to the use of these films in magnetic tapes or capacitors. In order to be used advantageously as a base for magnetic tape, polyester films must satisfy two requirements that have been found to be contradictory in practice. On the one hand, these films must have good slip properties in order for them to be used in industry, especially for winding them. On the contrary, a good quality magnetic tape should have a surface that is as smooth as possible, in order to avoid defects to the greatest extent possible when reproducing the recorded signals. In order to improve the slipperiness of films by reducing their coefficient of friction, one very often proposed solution is to introduce inert, generally inorganic fillers into the polyester. consists of things. Kaolinite, silica and other inorganic metal compounds or salts are commonly used for this purpose. However, the presence of these fillers on the surface of the film is disadvantageous at the magnetic tape stage. Currently, in the field of video, in particular, attempts are being made to produce magnetic tapes with a surface condition of the smallest possible defects, and for this purpose the base film itself is required to have an excellent surface condition, in particular for the final product. As quality demands increasingly low roughness, the presence of fillers on the film surface becomes even more troublesome. The roughness of a film is generally expressed by two values: - the total or maximum roughness, defined as the maximum depth of the roughness;
Value corresponding to R _t {“peak-to-valley”
- a value corresponding to the arithmetic mean roughness R _a {also called CLA, expressed in terms of Center line average;
Also called}, is. The total or maximum roughness R _t and the average roughness R _a are defined in Japanese Industrial Standard JIS B0601-1982, and methods for measuring them are described. Other fillers are also used, such as titanium dioxide, although titanium dioxide provides a relatively good compromise between coefficient of friction and roughness, since the addition of titanium dioxide causes the film to become cloudy to a considerable extent. Recovery may be economically necessary, but product waste is difficult to recover. Japanese Patent Application No. 87936 of 1975, which was published as Japanese Patent Publication No. 55-40929, has two different particle sizes.
The particles of the species population, i.e. some are 3-
It has been proposed to use inert fillers with a particle size of 6 microns, others essentially distributed in particle sizes from 1 to 2.5 microns. One object of the present invention is to use at least two particles as a filler, which have different properties and the particle size distribution of their respective particles does not necessarily have to be different.
It is an object of the present invention to provide a biaxially oriented film containing various inert inorganic compounds. More particularly, the present invention provides, based on the weight of the polyester, (a) an average particle size equal to 1 micron;
0.01% to 1% kaolinite below a micron; (b) average particle size equal to 1 micron;
The present invention relates to a biaxially oriented polyester film containing a filler, characterized in that it contains 0.01% to 1% of titanium oxide of less than micron size. Mean particle size is to be understood as the value of the diameter of a sphere corresponding to 50% of the volume of all particles, determined from the cumulative distribution curve of particle volume particle diameter. The spherical diameter of a particle is to be understood as meaning the diameter of a sphere having the same volume as said particle. The film according to the invention preferably contains kaolinite and titanium oxide having an average particle size of less than or equal to 0.7 micron. The polyesters used in the production of the film according to the invention are terephthalic acid, isophthalic acid, orthophthalic acid, naphthalene-2,5-dicarboxylic acid, naphthalene-2,6-dicarboxylic acid, naphthalene-2,7-dicarboxylic acid, succinic acid. dicarboxylic acids or lower alkyl esters thereof, such as sebacic acid, adipic acid, azelaic acid, diphenyldicarboxylic acid, and hexahydroterephthalic acid; and ethylene glycol, propane-
1,3-diol, butane-1,4-diol,
Neopentyl glycol and cyclohexane
Any known polyester obtained from one or more diols such as 1,4-dimethanol may be used. The polyesters commonly used are essentially homopolymers or copolymers containing alkylene terephthalate units. Preferably said polyester contains at least 80% by weight of ethylene glycol terephthalate units, more preferably at least 90% by weight of these units. The polyester may be a mixture of several homopolymers consisting of 80% by weight, preferably 90% by weight of polyethylene glycol terephthalate. The method for producing this type of polyester is known per se. Generally, the manufacturing method includes, for example, manganese acetate,
a step in which an interexchange (or transesterification) between a lower alkyl ester of terephthalic acid (such as dimethyl terephthalate) and ethylene glycol takes place in the presence of a catalyst such as calcium acetate or magnesium acetate. It will be done. It then comprises a step in which the polycondensation of ethylene glycol terephthalate is carried out in the presence of a catalyst such as an antimony or germanium oxide compound, and most commonly in the presence of a phosphorous compound such as phosphorous acid, phosphoric acid or esters thereof. It will be done. The fillers mentioned are preferably introduced during the polycondensation stage in the form of a suspension of particles in the diol used. Suspensions of this type are obtained simply by grinding the filler and ethylene glycol, and they can also be produced by grinding followed by centrifugation, which centrifuges the particles to achieve maximum particle size and particle agglomeration. Said filler suspensions from which substances can be removed can also be homogenized by known methods, such as for example by ultrasonic treatment. When producing the films according to the invention, in particular the following operating variants can be used: - The two fillers during the production of the polyester are introduced in the form of two suspensions in ethylene glycol. or alternatively, in the form of a common suspension of the two fillers in ethylene glycol, or - each filler is introduced in a different batch of polyester and the fillers thus obtained are Two polyesters containing kaolinite and titanium oxide, respectively, before extrusion (if necessary)
Mix with filler-free polyester. The latter variant uses only two batches of polyester containing one filler and, if necessary, no filler, containing respective proportions of kaolinite and titanium oxide according to the invention. It has the practical advantage of being able to produce films according to The weight ratio of kaolinite/titanium oxide in the film according to the invention varies within a wide range. usually,
This weight ratio is between 0.2 and 5. In the film according to the invention, the weight ratio of kaolinite/titanium oxide is preferably 0.5 to 2.
The total proportion of these fillers in the film is generally 0.05-1.2% by weight, based on the polyester. When these films are used for the production of magnetic tapes, 0.1 to 0.7% by weight of kaolinite+titanium oxide, based on the polyester, is preferred. The biaxially oriented polyester film according to the present invention can be produced by first extruding polyester to produce an amorphous film containing kaolinite and titanium oxide, and then stretching this amorphous film by a known method. . Stretching is carried out in sequential steps: first in the machine direction (longitudinal stretching) and then in a direction perpendicular to the machine direction (transverse stretching) or vice versa, ie transverse stretching followed by longitudinal stretching. Generally, longitudinal stretching is carried out at a ratio of 3 to 5 (i.e., the length of the stretched film is 3 to 5 times the length of the amorphous film) and a temperature of 80° to 100°C. , transverse stretching is carried out at a ratio of 3 to 5 and a temperature of 80° to 100°C. Stretching can be carried out simultaneously, ie simultaneously in the machine and transverse directions, for example at a ratio of 3 to 5 and at a temperature of 80° to 100°C. After stretching, it is heat set in a manner known per se, generally at a temperature of 180 DEG to 230 DEG C. Films produced in this way have a thickness of 1 to 50 microns, depending on their intended use. However, it is clear that thicker films can be made with the present invention if desired. The film according to the invention has good surface properties that allow it to be used even in demanding applications such as magnetic video tape. Total roughness as defined above of the film according to the invention
R _t varies from 0.05 to 0.5. The average roughness R _a , also defined above, is usually 0.05
There is a variation of ~0.5. Another important characteristic of the films mentioned above is the coefficient of kinetic friction μ _K , which makes it possible to evaluate the slipperiness of the films and thus their winding capacity under industrial conditions and, more generally, their mechanical suitability. The definition of this coefficient of kinetic friction μ _K and the method of measuring them are given on page 11 (item 3) of the European patent application published as no. 66997. The coefficient of kinetic friction μ _K of the film according to the invention is initially generally between 0.15 and 0.5. A property related to the film surface that is important to know is the peak height distribution (peak height distribution).
distribution) (i.e. PHD). For this purpose, it is first necessary to define the concept of peak. Within the scope of this invention, a peak will be defined as a protuberance on the film. Peak heights can be determined using any interferometrie methods suitable for this purpose.
It can be measured by For example, interferometric methods that allow the detection of phase amplitude can be used {see, for example, G. Roblin, J. Optics (Paris) 1977, No. 8
Please refer to Volume 5, pp. 309-318}. The interferometer is
It is used to measure peak heights and is conveniently used to estimate the number of peaks that have a height within the value of the fraction of wavelengths used for that measurement. The limits of this range, ie the extent of the range used for counting, can be changed and fixed as required. For example, it is possible to measure the number of peaks/mm ² within the following dimensions: −0.15 μm to 0.29 μm −0.25 μm to 0.44 μm −0.44 μm to 0.79 μm. Another important feature of the magnetic tape base and used is that it is defective due to the presence of peaks that are exceptionally high compared to other surface non-uniformities {the presence of these defects results in loss of information , hence the "dropout" in the case of magnetic videotape
It is well known that this can result in defects such as (drop out)}. The interferometric measurements described above are used to determine the number of defects with a height of 1 micron or more per cm ² of surface area. Finally, another property that characterizes films containing fillers is their haze measurement. This haze measurement is performed according to ASTM standard D1003. The haze of films containing titanium dioxide as filler is generally too high to permit recovery and use of these waste films, especially when they have to be recycled into packaging films. An indirect advantage of the film according to the invention is that, if desired, the overall proportion of filler can be reduced, thereby substantially reducing the haze value without increasing the coefficient of friction to an prohibitive degree. The point is that it can be done. In this way, filler-containing films can be produced that have a haze that is compatible with waste film recycling if desired. Another object of the invention is the use of the filler-containing biaxially oriented polyester film described above for the production of magnetic tapes. These tapes can be used in particular for recording sound recordings (audiotapes), recording images (videotapes) or recording various types of data (computer tapes). These magnetic tapes are obtained by coating the polyester film described above with a layer of a metal compound suitable for each application. The present invention also includes within its scope those magnetic tapes produced in such a manner from polyester films containing kaolinite and titanium oxide as fillers. Finally, the films according to the invention can also be used as dielectric layers in capacitors. The purpose of the following examples is to illustrate the invention without reducing its scope. Example 1 A Production of polyethylene glycol terephthalate containing titanium oxide as filler (a) Internal exchange 142.5 kg of dimethyl terephthalate was heated to 155°C.
So, 86.3Kg of ethylene glycol was heated to 110℃,
Charge the autoclave with 99.5 g of calcium acetate and 71.3 g of antimony oxide. The mixture is stirred and the methanol formed is distilled off. The amount of phosphoric acid necessary to prevent precipitation of calcium acetate in the polymer is then charged into the reaction mixture. 20% concentration by weight in ethylene glycol
3.5Kg of TiO ₂ suspension is then added. The suspension is manufactured as follows: - The following materials are mixed cold in a turbine paste mixer for 1 hour: HOMBITAN LW-S from SACHTLEBEN.
TiO ₂ 62Kg, ethylene glycol 56Kg, -This suspension is running continuously 2
Final dispersion is achieved by successive passes through a base ball mill (filled with balls of diameter 1 and 1.5 mm). - the ground suspension is then diluted to 20%, and - the suspension is stored with stirring. This _TiO2 has an average particle size of 0.4 microns. The average particle size of the suspended filler was determined using a HORIBA type Capa500 particle size analyzer operated by centrifugation. After introducing the TiO ₂ suspension, excess ethylene glycol was added until the temperature of the reaction mixture was 260 °C.
Distilled until reaching ℃. The resulting mixture is filtered and then transferred to a polycondensation autoclave. (b) Polycondensation Autoclaves for polycondensation contain a stirrer. Polycondensation starts at 265°C. The apparatus is placed under vacuum (40 mm of mercury, then 1 mm). The polycondensation is continued until a polyester having an intrinsic viscosity of 0.65 dl/g (measured in a 1% strength solution in orthochlorophenol at 25° C.) is obtained. The polyethylene terephthalate () obtained is drained and extruded in the form of granules.
This material is based on the actual polymer 0.05
Contains % _TiO2 by weight. B. Polyethylene glycol terephthalate containing kaolinite as filler Same as method A, except that the kaolinite suspension is manufactured as follows: Load into the mill: -28.5 Kg ethylene glycol, -19 Kg HG90 Kaolin HUBER, -30 Kg dispersant. Continue milling for 1 hour. The ground suspension is filtered and the filtrate is diluted with ethylene glycol to a concentration of 15% by weight and heated. The diluted kaolinite suspension is centrifuged in a centrifuge with a bowl mouth having a G value of 4500 or higher. The concentration of kaolinite in the suspension leaving the centrifuge is 10% by weight. The kaolinite suspension produced in this way is introduced into an internal exchange autoclave in the same way as the TiO ₂ suspension. Two batches of polyethylene glycol terephthalate containing kaolinite as filler are produced: - a batch containing 0.40% by weight of kaolinite based on the polymer (the average particle size of the kaolinite used is 0.5 micron); - a batch containing 0.40% by weight of kaolinite based on the polymer (the average particle size of the kaolinite used is 0.6 micron). C. Production of filler-free polyethylene glycol terephthalate (PET) The method is the same as above, but no filler is added to the polymer. This is a batch of PET containing no filler. Examples 2-8 Various films were extruded starting from various relative proportions of the polymer(s) and/or and as described above. Intimate mixing of the polymer is achieved when loading the granules into the extruder. After extruding the amorphous film, initially about 3.7
Longitudinal stretching at a ratio of 90°C, then a ratio of approximately 3.7, 110
Laterally stretched at ℃. The film thus obtained is heat set at 210°C. The thickness of these films is approximately 14.5 microns. Measurements performed on these films were: (1) Trademark with FT25 external reference probe (diamond radius of curvature: 3.5 microns);
PERTHEN's perthometer
Measurement of roughness (total and average) using: - probing length: 1.5 mm, - cutoff filter wavelength: 0.08 mm. (2) Haze measurement using a GARDNER trademark haze meter. (3) Measurement of the coefficient of kinetic friction μ _K by the method shown in the explanation.
μ _K is measured by running a 25 mm wide strip of film over a fixed metal roller with a diameter of 25 mm and a roughness R _t equal to 0.3 microns. The running speed is 5 m/min, and the length of the film to be tested is 100 to 150 m. (4) Measurement of PHD: This is done by the method described in the Description section. Controls a, b and c, and Examples 2, 3,
Films corresponding to Nos. 4, 5, 6, 7 and 8 are prepared and tested in this manner. The characteristics of these films and the relative properties of the polymer(s) and/or used to make these films are contrasted in the following table.

【table】

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Claims (1)

Claims: 1. Based on the polyester: (a) 0.01 to 1% by weight of kaolinite having an average particle size of less than or equal to 1 micron;
(b) 0.01 to 1% by weight of titanium oxide having an average particle size of less than or equal to 1 micron. 2. Less than 0.7 microns or 0.7
A film according to claim 1, characterized in that it contains kaolinite having an average particle size equal to microns and titanium oxide having an average particle size less than or equal to 0.7 microns. 3. The polyester according to claim 1 or 2, characterized in that said polyester is a homopolymer or a copolymer containing at least 80% by weight, preferably at least 90% by weight of ethylene glycol terephthalate units. film. 4. The film according to claim 1, wherein the weight ratio of the kaolinite and the titanium oxide contained in the film is 0.2 to 5. 5. The film according to claim 1, wherein the weight ratio of the kaolinite and the titanium oxide contained in the film is 0.5 to 2. 6. The total proportion of kaolinite and titanium oxide contained in said film is from 0.05 to 1.2% by weight, based on said polyester, preferably from 0.1 to 0.7% by weight, based on said polyester. The film according to item 1 of ranges 1 to 5. 7 Based on the polyester: (a) 0.01 to 1% by weight of kaolinite with an average particle size less than or equal to 1 micron;
(b) 0.01 to 1% by weight of titanium oxide having an average particle size of less than or equal to 1 micron. The film is prepared from a mixture of two batches of polyester, one batch of polyester containing titanium oxide and another batch of polyester containing titanium oxide as a filler, and optionally a batch of polyester containing no filler. The method characterized in above. 8 Based on the polyester: (a) 0.01 to 1% by weight of kaolinite with an average particle size less than or equal to 1 micron;
and (b) 0.01 to 1% by weight of titanium oxide having an average particle size of less than or equal to 1 micron. , a batch of polyester containing both kaolinite and titanium oxide.